It is known that alkyl chloroaromatic compounds having one or more hydrogen atoms attached to the .alpha.- carbon atoms of the side chain are reactive when treated with chlorine in the presence of ultraviolet radiation. Under such conditions, substitution of one or more of these hydrogen atoms, often referred to as benzylic, or .alpha.-hydrogen atoms, by chlorine, normally occurs. It is also known that it is difficult to limit replacement to only one of these hydrogen atoms with chlorine under these conditions, since a second and often a third hydrogen atom may also be replaced, giving rise to the formation of a mixture of mono and poly.alpha.-chlorinated alkyl aromatic compounds. From a commercial point of view such prior art processes have serious drawbacks where the objective is the preparation of the commercially desirable mono.alpha.-chlorinated compound. The mono .alpha.-chlorinated products are of commercial importance as intermediates in the production of pesticides and in the preparation of quarternary ammonium compounds for use as disinfectants and the like. The formation of mixtures of mono and polychlorinated compounds requires additional separation steps to isolate the desired .alpha.-chlorinated compound, thus adding to the complexity and cost of the process.
One solution to this problem in the prior art processes has been to minimize the formation of poly .alpha.-chlorinated compounds by greatly limiting the degree of completion to which the chlorination reaction is carried. However, although this practice minimizes the formation of poly .alpha.-chlorinated compounds, it has the disadvantage of requiring a large amount of recycle thus making the process inefficient and more expensive.
Accordingly, it is a primary object of this invention to provide an improved process for the selective mono .alpha.-chlorination of alkyl chloroaromatic compounds. It is a further object to provide such a process whereby the formation of polychlorinated compounds is minimized, allowing the chlorination reaction to be carried more nearly to completion than is feasible in the prior art processes. It is a still further object to provide a catalytic process for the selective mono .alpha.-chlorination of alkyl chloroaromatic compounds that may be carried out in the absence of ultraviolet radiation. Additional objects and advantages of the present invention will become apparent to those skilled in the art from the following description.